Li Atoms Research Articles

Synthesis and Structures of Oxide -Centred Alkali Metal (K, Li)/Lanthanoid (Ln3 or 4) 3,5-Dimethylpyrazolate Cages - Herbert Schumann Revisited.

Reaction of lanthanoid tris(3,5-dimethylpyrazolate) compounds, [Ln(Me2pz)3(thf)]2 (Ln=La 1 a, Ce, Pr, Dy 1 b, Yb, Lu) with potassium or lithium bistrimethylsilylamide and with or without added 3,5-dimethylpyrazole, or of lanthanoid tris(bistrimethylsilyl)amide complexes with potassium bistrimethylsilylamide and 3,5-dimethylpyrazole have yielded a variety of oxide centred Ln3 or Ln4/(K or Li)1-3 multinuclear cages, namely, [La4O(Me2pz)11 K(thf)2] (2 a), [La4O(Me2pz)11Li(Me2pzH)]⋅0.5Hexane (2 b), [La4O(Me2pz)10(Me2pzH)] (2 c) (from heating 1 a in toluene), [Ce3O(Me2pz)9K2(dme)2] (3 a), [Ce3O(Me2pz)9Li2(thf)2]⋅0.5Hexane (3 b) and [Ce(Me2pz)5Li2(thf)3] (3 c), which crystallized together, [Ce3O(Me2pz)10K3(thf)3] (3 d), [Pr3O(Me2pz)10K3(thf)3] (4), [Dy3O(Me2pz)9K2(thf)2]⋅THF (5), [Yb3O(Me2pz)9K2(thf)2]⋅THF (6), and [Lu3O(Me2pz)9K2(thf)2]⋅THF (7). Crystals of {[K8(Me2pz)8(thf)2]⋅THF}∞ (8) were also obtained from the preparation of 7. From reaction of [Ce(Me2pz)3(thf)]2 with potassium tert-butoxide in toluene, the cerium(IV) heterobimetallic polymer [Ce2(Me2pz)6(OtBu)4K2]∞ (9) was isolated. In the Ln3O and the Ln4O cages, the Ln atoms have triangular and distorted tetrahedral arrangements about the central oxygen, respectively. The relationship of the alkali metals to the central oxygen varies considerably. Thus in 2 a, 2 b, there is no bonding, in 3 a, both K atoms interact weakly, in 3 b one of the two Li atom is bound, in 3 d, 4, one of three K atoms in bound, whilst in 5-7, both K atoms are bound. All metals are bound to the cages by a variety of pyrazolate binding modes, with up to five different exhibited in some structures, and a new coordination mode, μ4-1κ(N):2κ(N'):η5:η5, was observed in two complexes. In the structure of 2 c, the coordinated Me2pzH ligand binds to two metals through a single nitrogen, the first time this has been observed for a pyrazole donor. The complex 9 is polymeric with all metals bridged by butoxide donors as well as by Me2pz groups.

Half‐Heusler Alloy CoMnZ (Z = Sb/Sn): Electrode Material for Lithium‐Ion Batteries

ABSTRACTHeusler alloys (HAs) are a well‐known family of compounds generating promising interest due to their robust structure, ease of tailoring their unique properties, and potential applications. The investigations in the direction of the electrochemical performance of these materials as electrodes for rechargeable lithium‐ion batteries (LIBs) have been established theoretically and experimentally. Alloying of alkali metal ions into half‐HAs unit cells can be another route to improve LIBs performance. This work presents our investigations on thermodynamically stable half‐HAs CoMnZ (Z: Sb/Sn) as electrode materials for rechargeable LIBs using the first‐principle calculations based on the density functional theory. The negative formation energies validate the thermodynamic stability of the alloys considered in this study. With increasing Li doping, a structural change from cubic to tetragonal and orthorhombic phase is observed in the host structure, and upon full lithiation (LiMnZ), a cubic structure is attained. The band structure calculations of the host structure and its lithiated phase indicate a metallic nature in these alloys. The calculations are also performed to investigate the structural stability of parent alloys and corresponding lithiated phases. We calculated a storage capacity of around 14.5 Ah/kg for 0.125 atomic fraction of Li atoms, which is increased by nearly 10 times upon full lithiation. A maximum open circuit voltage of around 9.8 V is calculated for Li0.125Co0.875MnSb and CoLi0.125Mn0.875Sb. Thus, all these remarkable results suggest that these intermetallic compounds have a strong potential as the cathode material for LIBs with a robust life and a large capacity.

Cs3LiGe4, One Compound with Two Complementary Structural Descriptions: Isolated [Ge4]4- Tetrahedral Clusters Coordinated by Li+ and Cs+ Cations or One-Dimensional [LiGe4]3- Polyanions Packed within a Matrix of Cs+ Cations?

Reported are the synthesis and structural characterization of Cs3LiGe4, the first structurally characterized lithium-containing cesium germanide. Single-crystal X-ray diffraction data indicate that Cs3LiGe4 crystallizes in an orthorhombic crystal system with the space group Cmcm (no. 63, Person symbol oS32) with unit cell parameters a = 6.950(2) Å, b = 15.503(3) Å, and c = 9.919(2) Å and V = 1068.65(4) Å3. The structure consists of [Ge]44- tetrahedral clusters with the Li atoms positioned in such a way that polyanionic [LiGe]43- chains could be considered as well. Electronic structure calculations indicate an intrinsic semiconductor with a band gap of 0.76 eV. To understand the nuances of the chemical bonding, position-space techniques based on the quantum theory of atoms in molecules, the electron localizability indicator, and their basin intersections were employed confirming the covalent character of the Ge-Ge bonding. The strong polarity of the interactions between [Ge]44- and the surrounding lithium and cesium cations suggests to interpret these as mainly ionic, further supporting the most basic structure rationalization [Cs+]3[Li+][Ge]44-, following the Zintl-Klemm concept. The electron localizability indicator topology affirms the striking similarities between [Ge]44- and molecular As4 tetrahedra in yellow arsenic, further supporting Klemm's pseudoatom concept on a quantum chemical basis.

Conductivity Prediction Method of Solid Electrolyte Materials Based on Pearson Coefficient Method and Ensemble Learning

In order to screen solid electrolytic materials with high ionic conductivity more quickly and accurately, a conductivity prediction method for solid electrolyte materials based on logistic regression model and random forest regression model is constructed. The method first selects 20 characteristic descriptors related to ionic conductivity from material library according to four dimensions: structural stability, metal stability, electronic conductivity and oxidative decomposition stability. The enumeration method and feature selection method are used to combine different features. Then, the dimension reduction of the feature combinations is carried out by Pearson coefficient method, so as to screen the optimal feature combinations. Finally, according to the optimal feature combination and data subset, the constructed random forest ensemble learning model is utilized to predict the ionic conductivity of other solid-state electrolyte materials in the material library, in order to find the solid-state electrolyte materials that can meet the high conductivity. The results indicate that as the number of features in the combination increases, the prediction performance of the model shows a trend of first increasing and then decreasing. When the feature descriptor in the combination is 7, the maximum AUC (Accuracy) value is reached, and the optimal feature in this case contains 7 optimal feature subsets corresponding to feature descriptors, namely the standard deviation of the average adjacency number of Li atoms, the standard deviation of Li-X ion bonds, the average electronegativity of the straight path, the average width of the straight path, the average atomic volume, the average Li-Li bond, and the filling fraction of the sublattice. On the basis of the optimal feature screening, the average prediction accuracy of the logistic regression model is 87.13%, which has a high accuracy. Using the random forest regression model for prediction, the average absolute error and root mean square error obtained are only 0.237 and 0.134, and compared with classical classification methods such as KNN, SVM and Adaboost, they are smaller, which can better predict the ionic conductivity of solid electrolyte materials. This proves that the constructed method can quickly and accurately produce high ionic conductivity materials in solid electrolyte materials, which is worthy of further research and promotion.

Facile synthesis and first principles calculations of Li-MoS2/rGO nanocomposite for high-performance supercapacitor applications

Two-dimensional (2D) nanostructured materials such as graphene oxide nanosheets and molybdenum disulfide (MoS2) are potential candidates for electrochemical energy storage applications. The layered structure of MoS2 makes it a promising active electrode material for supercapacitors. Lithium (Li) interacted with MoS2/reduced graphene oxide (Li-MoS2/rGO) nanocomposite has been synthesized in two steps using a sonochemical dispersion method, and a one-pot hydrothermal method resulting in few-layered MoS2/rGO nanosheets of 2D heterointerfaces. The Li-MoS2/rGO nanocomposite exhibits a high specific capacitance of 173.3 F g−1 at a current density of 1 A g−1. Furthermore, an asymmetric supercapacitor device fabricated with Li-MoS2/rGO achieves a good energy density of 10.6 Wh kg−1 at a power density of 686.3 W kg−1 and outstanding cycling stability with 81.2 % capacity retention over 10,000 cycles. The dispersion of 2D-MoS2 in water is due to the strong electrostatic interface. The structural and electronic properties are theoretically calculated for pristine and Li-interacted MoS2/rGO heterostructure using density functional theory. A comparison of the density of states plots of the two heterostructures and the difference charge density plot of Li-MoS2/rGO heterostructure clearly brings out the importance of the presence of Li. A value of 64 μF cm−2 for the quantum capacitance for pristine MoS2/graphene heterostructure increases to a value 99 μF cm−2 corroborating the experimental observations and we assign this change to the transfer of charge from the Li atom to the outer S atoms in the MoS2/graphene heterostructure. This comprehensive approach, combining experimental synthesis with computational modelling, significantly advances the development and optimization of high-performance supercapacitor materials in the energy storage field. The Li-MoS2/rGO nanocomposite has excellent electrochemical specific capacitance and long-term cyclic stability and has been effectively used for supercapacitor applications with high electrochemical performance.

First-principles study on the lithiation process of amorphous SiO anode for Li-ion batteries with Bayesian optimization.

Amorphous silicon monoxide (a-SiO), which contains Si atoms with various valence states, has attracted much attention as a high-performance anode material for lithium (Li) ion batteries (LIBs). Although current experiments have provided some information during charge/discharge cycles, further investigation of structural changes at the atomic scale is needed. To investigate the lithiation process of a-SiO using first-principles simulations and machine learning techniques, we developed a computational code employing Bayesian optimization to efficiently identify stable sites for Li insertion in the large search-space of amorphous models to reproduce the actual lithiation process and compared this approach to the conventional random scheme by applying it to an a-SiO model previously generated with neural network potentials. The lithiation process based on Bayesian optimization resulted in lower formation energies compared to the conventional random scheme, indicating a more stable structure. During lithiation, Li atoms tended to enter the silicon (Si) phase after the SiO2 phase, in agreement with experimental results. We analyzed the structural changes and observed significant differences in the structural evolution between the conventional and new schemes. Our study highlights the significant influence of the lithiation process on the structural transformation of a-SiO materials, which in turn affects the reversible capacity of the material. These findings will provide a framework for improving the performance and lifetime of a-SiO materials.

Single‐Crystalline LiMg Alloy Anode for Deep Cycling All Solid State Lithium Metal Batteries

AbstractAll solid state lithium metal batteries (ASSLMBs) with enhanced energy density has driven the exploration of Li‐alloy anodes such as Li‐Mg alloy owing to its solid‐solution structure and high theoretical specific capacity. But the Li atom diffusion limitation on Li‐Mg electrode surface further leads to sluggish atoms transport dynamics. Herein, single‐crystalline (110)‐oriented Li0.9Mg0.1 (denoted as LiMg(110)) anode is obtained by a tailored melt‐annealing procedure to tackle the above issues. Theoretical analyses and experimental results demonstrate that the crystallographic structural (110) orientation of LiMg anode can facilitate Li atom diffusion and guarantee the electrode stability during deep cycling. As a result, the LiMg(110) electrode exhibits longer cycle life with lower overpotential than polycrystalline LiMg at high current densities and areal capacities in symmetric cells. A critical current density (CCD) at the forefront of 2.5 mA cm−2 is achieved in Li3InCl6 (LIC) solid‐state system. The ASSLMB with high areal capacity (3.8 mAh cm−2), high current density (0.76 mA cm−2), and low negative/positive capacity N/P ratio (2.14) achieves exceptional cyclability over 160 cycles. The outcomes highlight a promising crystallographic regulation strategy toward practical applications of high‐performance lithium metal batteries.

DFT and AIMD Evaluation of Boron‐Doped Biphenylene as an Anode Material in Lithium‐ and Sodium‐Ion Batteries

AbstractDesign and proposal of high‐efficiency anode materials are crucial for the development of batteries with enhanced power and energy density, a key factor in their commercialization. This study presents a comparative theoretical study to evaluate the potential of boron‐doped biphenylene (B‐BP) as an anode electrode in lithium‐ion batteries (LIBs) and sodium‐ion batteries (SIBs). Current research investigates the impact of boron doping on the structural, electronic, and stability properties of pristine biphenylene. Computational calculations reveal strong interactions between charge carriers (Li and Na atoms) and the proposed anode with a charge transfer from Li/Na atom to the surface. According to kinetic studies, a low energy barrier for charge carrier diffusion has been obtained which makes it a promising candidate for fast‐charge battery applications. Theoretical capacity calculations show that B‐BP outperforms graphite as the commercial case of anode material, with calculated values of 560.67 mAh g−1 for Li and 934.45 mAh g−1 for Na storage.

Li decorated graphdiyne nanosheets: A theoretical study for an electrode material for nonaqueous lithium batteries

In this work, Density Functional Theory (DFT) is used to study pristine and defective GDY. We investigate the effect of Li atom adsorption on the electronic and structural properties of this 2D material. In both cases, the Li atom is located at the corner of the triangular‐like pore (H1), but with a slight shift for the defective system. In the perfect system, the Li‐C bond distances range from 2.289 Å to 2.461 Å, while in the defective case, they range from 2.237 Å to 3.184 Å. In the perfect case, the GDY‐Li system becomes metallic and the Li 2s states are stabilized. Charge transfer to the surfaces occurs near the vicinity of the Li atom. The C vacancy generates new C=C bonds similar to double bonds, enhancing the interaction with Li through strong conjugation. After Li adsorption, the sum of bond order for all the C atoms increases in both structures, from 0.4% to 6%. The Li storage capacity without significant restructuring is six Li atoms. When the atom concentration increases, the OCV values for Li decrease from 0.93 V to 0.23 V. For defective GDY, the specific capacity is 788 mAhg‐1, which is slightly higher than for pristine case.

A comprehensive theoretical scheme for understanding the core structure and the mechanical behavior of basal dislocations with solute atmosphere in Mg alloys

The basal dislocations play a key role in the deformation of hexagonal Mg alloys. However, its core structure and mechanical behavior have thus far not yet been understood adequately, largely owing to the fact that the basal dislocation, often decorated with segregated solute atmosphere and dissociated into two partials, cannot be modeled accurately. Significant discrepancies exist between theoretically calculated and experimentally observed structures for these dissociated dislocations. Here we present a comprehensive theoretical scheme to model them in the Mg alloys with alloying elements of Y, Zn, Al and Li, respectively. Firstly, solute–dislocation interactions were computed by appropriate first-principles calculations. Secondly, the statistic solute concentration at a dislocation is estimated by a Fermi–Dirac distribution. Finally, all these effects on dislocations are integrated into an improved two-dimensional Peierls–Nabarro model to predict their core structures and mechanical behaviors in Mg alloys. It is shown that although Zn, Al and Li atoms have little effect on basal dislocations, Y atoms can largely increase their dissociated width. Furthermore, when it moves from its ground state configuration, the dissociated dislocation can further be widened, such that its dissociated widths in a Mg–0.8Y (at%) alloy at 300 K can reach 12–36 nm, in rather good agreement with the experimentally observed values of 20–30 nm. Besides, the Peierls and yield stresses of Mg alloys shall increase with increasing added solute concentration, while they are decreased drastically with increasing the temperature from 300 to 800 K, but with the Mg-Y alloy as somewhat exception, which is again consistent with experimental observations.

Transition-metal-based hydrides for efficient hydrogen storage and their multiple bond analysis: A first-principles calculation

Hydrogen energy plays a growing role in the present energy market and attracts more attention in scientific researches and commercial application. Hydrogen energy has an increasing attractive in energy market due to its high energy density, pollution-free utilization usage and wide availability. Current challenge which obstructs large-scale application is safe and reliable hydrogen storage, which requires finding promising materials to promote hydrogen energy. Therefore, we have predicted three potential lithium-transition metal-based hydrides LiTM3LiH8 (TM = Sc, Ti V) for hydrogen storage based on first principles calculation. The stability analysis based on formation energy, elastic constants and phonon spectra confirms all hydrides are stable and feasible in practical application. Besides, they have a increasing ductility in the order of Sc, Ti and V. Among all studied materials, LiV3LiH8 has the best mechanical characteristics due to its excellent ductility and high Young's modulus (123.19 GPa), which are beneficial for resistance to adverse external surroundings. The electronic properties suggest that all hydrides metallic in band structures. Meanwhile, we analyzed how hydrogen was storage and the binding information from multiple perspectives, including the charge analysis, DOS, ELF and COHP. From multiple analyses of bond strengths, except the strong binding from transition metal, the centered Li atom is verified to possess greater influence than corner Li atom, which makes a viable regulation of hydrogen properties by substituting centered alkali metal atom in future. As concluded in this study, LiTi3LiH8 has a high storage capacity of 4.83 wt% along with a desorption temperature of 305.5 K, which is considered as a promising hydrogen storage material.

Cs/O, Cs/NF3, and Cs/Li/NF3 coadsorption on GaAs0.5P0.5 (001) β2(2×4) reconstruction surface: A first principle study

The activation process of p-type doped GaAs0.5P0.5 (001) β2(2 × 4) reconstruction surface is investigated based on first principle calculations. For Cs-only adsorption, the adsorption energy rises as the Cs coverage increases, and when the Cs coverage is at 0.75 ML, the work function hits its minimum. Cs/O and Cs/NF3 concurrent adsorption are conducive to increasing steadiness and lowering the work function of the reconstruction surface during the phase of high Cs coverage. The work function reaches its minimum when Cs coverage is 0.75 ML in Cs/O coadsorbed models while that occurs when Cs coverage is 1.00 ML in Cs/NF3 coadsorbed models. Results indicate that the Li atoms intercalation with low coverage in Cs/NF3 coadsorbed models is conducive to establishing dipole moments, strengthening stability, and lowering the work function. The optimal adsorption recipe is 6Cs/2Li/NF3, with which the surface owns the lowest work function and shows the most stable property.

A theoretical exploration of the electronic structure and single photoionization of the many-electron system confined in Gaussian potential

This manuscript investigates the electronic structures, spectral properties, and photoionization processes of the confined atomic system. For this purpose, a relativistic methodology employing the Dirac–Coulomb Hamiltonian within the context of relativistic configuration interaction is suggested, utilizing independent particle basis wavefunctions. The key idea of this approach is to place the atom inside a Gaussian potential, which gives a realistic description of the spatial confinement in quantum dots due to a smooth change at the quantum dot boundaries and has a finite range and depth for the spatial confinement. As a result, the local central potential is modified, which is determined by a self-consistent process. The solutions to the Dirac equation, incorporating the aforementioned central potential, yield both the continuous and bound state wave functions. The photoionization process is determined through the application of the distorted wave approach within the context of relativistic Dirac theory. As an application, the electronic structures of the confined Li atom, including energies, ionization potentials, transition rates, and photoionization dynamical properties such as wave functions, cross sections, and photoelectron angular distributions, are systematically investigated within the dipole approximation for a wide range of potential depths and confining radii. A systematic comparison of the present outcomes is made with other available results. The present study is not only meaningful for fundamental research in atomic and molecular physics, but also has implications for a range of disciplines, such as nanochemistry, materials science, and other related fields.

Be/Li doped C24 and C12B12 nanocages for hydrogen storage: A comparison

The hydrogen storage on Be/Li doped C24 and its boron substituted derivative(C12B12) is studied using density functional theory(DFT). Doping of four and six Be atoms on tetragonal rings of C24 and C12B12 nanocage, respectively is possible. This difference is due to lower(higher) binding energy of Be atoms with C24(C12B12) than its cohesive energy in bulk. Doping of six Be atoms on C24 disturbs the cage. Doping of six Li atoms on tetragonal rings of C24 and C12B12 is possible without disturbing the cage as binding energy of Li atoms with both the cages is higher than its cohesive energy in bulk. Metal doped C12B12 shows higher H2 uptake capacity than C24. H2 molecules interact more strongly with Be doped nanocages than Li doped nanocages. The metal atoms bind more strongly with C12B12 nanocage than C24. From formation energy, metal doped C12B12 are more stable than metal doped C24. Though Li doped nanocages show higher H2 uptake capacity, they are not suitable for hydrogen storage at ambient conditions. Be doped nanocages are more suitable for hydrogen storage at ambient conditions.

Compositional Engineering of Lithium Metal Anode for High-Performance Garnet-Type Solid-State Lithium Battery.

Garnet-type solid-state lithium batteries (SSLBs) possess excellent potential owing to their safety and high energy density. However, fundamental barriers are deficient cycling stability and poor rate capability. The main concern lies in generating voids at the Li|garnet interface during Li stripping, stemming from the sluggish diffusion of Li atoms inside the bulk Li metal. Herein, a composite anode (AN@Li) containing Li-Al alloy, Li3N, and LiNO2 is designed by introducing aluminum nitrate into molten Li. The lower interfacial formation energies exhibited by Li-Al alloy, Li3N, and LiNO2 with garnet solid-state electrolyte (SSE) enhance the wettability of AN@Li toward SSE. Meanwhile, it affords efficient conductive pathways that facilitate Li+ diffusion in the bulk anode (not just on the surface). Impressively, the resulting symmetric cell with AN@Li electrodes achieves high critical current density (1.95mA cm-2) and long cycle life (6000h at 0.3mA cm-2). The SSLB coupled with LiFePO4 cathode and AN@Li anode enables stable cycling for 200 cycles at a high rate of 1 C with a retention of 96% and exhibiting outstanding rate capability (145.9 mAh g-1 at 2 C). This work provides practical insights for producing high-performance lithium metal anode for advanced garnet-type SSLBs.

DFT insight into the structural, vibrational, and electronic properties of thin [110] Ge nanowires as anodic material for Li batteries

Germanium nanowires could be used to improve as anodic materials since their charge rate is better than that of the current graphite electrodes. In this work, we present a Density Functional Theory study of the effect of interstitial Li atoms on the vibrational, electronic, and mechanical properties of ultrathin hydrogen-passivated Ge nanowires (HGeNWs) with diamond structure, grown along the [110] crystallographic direction, and with a diameter of ∼14.4 Å. The interstitial Li atoms were placed at the tetrahedral positions (Td) reported as the more favorable ones. The phonon band structure of the HGeNWs reveals the existence of high frequency vibrations due to the hydrogen atoms at the nanowire surface. The effect of one interstitial Li atom in the nanowire leads to the apparition of three flat phonon bands almost independent of the collective vibrational states of the nanowire, reflecting a weak interaction between the Li atom and the neighboring ones; and a shift of the high vibrational modes to lower frequencies that results in more dispersive states. The electronic band structure confirms a transition from semiconducting to metallic behavior by adding a single Li interstitial atom per unit cell. The formation energies indicate that the nanowires with interstitial Li atoms are stable, and the average binding energy per Li atom slightly increases as a function of the concentration of Li atoms. The insertion of Li atoms in the nanowire leads to a volumetric expansion, without fracture or broken bonds. Even more, the redistribution of the electronic charge due to the Li atoms give the Ge-Ge bonds more axial elasticity and the values of the modulus of Young are almost constant for all studied concentrations of Li atoms. These theoretical results indicate an improvement of mechanical and electronic properties of Ge nanowires through the addition of interstitial Li atoms that could be important for their use as anodes in rechargeable Li batteries.

Significant promotion of interlayer ion diffusion for MoS2 /MoBS heterostructure as high performance Li/Na ion batteries anode material

As a member of the new two-dimensional materials family, functionalized MoB (MBene) attracts great interest as energy storage materials due to their excellent mechanical properties and metallicity. Here, we aim to leverage the superior properties of MBene to develop new promising electron materials for Li/Na-ion batteries by designing the MoS2 /MoBS heterostructure. Our investigation focuses on the structural stability, mechanical and electrochemical properties by first-principles calculation. The high Young's modulus, robust structural stability and metallicity prevent the electrode pulverization and guarantee cycle stability of battery. Impressively, the interlayer diffusion barriers of Li and Na atoms are only 0.26 and 0.16 eV, outperforming other MoS2-based heterostructures. With calculated open circuit voltage of 0.01–1.83 V for Li atoms and 0.02–1.28 V for Na atoms, the heterostructure is suitable for deployment as an anode material. Besides, the reversible specific capacity (376 mAh/g) of Li atoms is improved by the electron transfer caused by the formation of heterostructure compared to that of monolayer MoS2 (335 mAh/g) and MoBS(193 mAh/g). These findings fully underline the potential of MoS2/MoBS heterostructure as anode material of Li/Na-ion batteries.

The dominant roles of “electron-density-mechanism” and “chemical-bonding-mechanism” for hydrogen in molybdenum and lithium

Using first-principles calculations, we have systematically studied structures and thermodynamic stability of interstitial H as well as the H-vacancy interaction in molybdenum (Mo) and lithium (Li). Single H atom prefers to occupy tetrahedral interstitial position (TIP) and octahedral interstitial position (OIP) in Mo and Li, respectively, and the solution energies are 0.87 eV and −0.66 eV, respectively. In Mo, mono-vacancy can capture as many as seven H atoms and each H atom prefers to bind onto an isosurface of valence electron density. However, H atoms detach from vacancy to occupy the OIPs outside vacancy in Li. Based on these results, we reveal that the electron-density-mechanism (EDM) and chemical-bonding-mechanism (CBM) cause different properties of H in Mo and Li, respectively. In Mo, since the valence electron density everywhere in interstitial lattice is much high, H atom has to search a place where the valence electron density must be suitable. Accordingly, vacancy can provide an optimal valence electron density region for H dissolution, and the optimal valence electron density is 0.10 electron/Å3 at vacancy. In Li, H atom exhibits the negative solution energy in the interstitial lattice, which promotes H atom to form ionic bond with neighboring Li atom. H atoms do not combine inside vacancy but stay at the OIPs outside vacancy to form ionic bonds with neighboring Li atoms. We believe that the EDM and CBM can be generalized to other transition metals and other alkali metals, respectively.

Bilayer graphene, bilayer GeC and graphene/GeC bilayer heterostructure as anode materials for lithium-ion batteries: First-principles calculations

There is a great effort to develop the high-efficient anode materials for lithium-ion batteries with high stability and mobility. In this paper, we adopt the first-principles calculations to study the electrochemical properties of Li intercalation within bilayer graphene (BLG), bilayer GeC (BLGeC) and graphene/GeC bilayer heterostructure (BLGGeC) as anode materials. Our calculations disclose the following findings: (1) The interlayer is modulated by the stacking patterns and bilayer species. (2) The most energetically favorite intercalation of the Li atom is achieved in BLG with AA stacking because of the lowest adsorption energy. (3) The descending order of energy barriers is BLGGeC > BLGeC > BLG. The low diffusion barriers of BLG (0.025 eV) and BLGeC (0.09 eV) imply their high charging/discharging rates. Finally, the findings underline that the bilayer is a promising anode material and its electrochemical characteristics can be changed by adjusting the stacking configurations and its species.

Exact Theory Applied to the Lithium Atom.

The free complement (FC) theory for solving the scaled Schrödinger equation (SSE) was applied to the Li atom for calculating the exact wave functions, the energies, and the various properties of the ground doublet S and excited P states. The SSE is equivalent to the Schrödinger equation (SE) but does not have the divergence difficulty of the variational equation of the SE. Because the Li atom is a three-electron system, the variational exact FC calculations for solving the SSE are possible using the function g = 1 - exp(-γr) as the "correct" scaling function of the SSE. The "reasonable" scaling function g = r was also used as comparative calculations. We performed variational calculations to the order eight of the FC theory and could obtain essentially exact solutions of the SSE or SE with the "correct" g function of the FC theory. We report here the values of the exact energy, spin density, electron density, and electron-nuclear and electron-electron cusp values of the doublet S and P states. They agreed very well with the experimental values and the best theoretical values presented by Drake and collaborators. This is a simple example that the exact theory gives the exact solutions.